We present high-resolution images of the strongly bipolar planetary nebula NGC 6537 , obtained with Hubble Space Telescope and with the infrared adaptive optics system on the Very Large Telescope .
The central star is detected for the first time .
Using the multi-band photometry and constraints from the dynamical age of the nebula , we derive a temperature in the range 1.5–2.5 \times 10 ^ { 5 } K , a luminosity \sim 10 ^ { 3 } L _ { \odot } , and a core mass M _ { c } \approx 0.7 – 0.9 M _ { \odot } .
The progenitor mass is probably in the range M _ { i } = 3 \hbox { - - } 7 M _ { \odot } .
The extinction map shows a largely symmetric , and compact dust structure , which is most likely a shell , located at the neck of the bipolar flow , only 2–4 arcsec from the star .
The dust shell traces a short-lived phase of very high mass loss at the end of the AGB .
The dynamical age of the shell and bipolar lobes are very similar but the morphologies are very different .
The data suggests that the mass loss during the ejection of the compact shell was largely spherically symmetric , and the pronounced bipolarity formed afterwards .
The dynamical ages of the bipolar lobes and dust shell are similar , which is consistent with suggestions that bipolar structures form in a run-away event at the very last stages of the AGB mass loss .
The inner edge of the dust shell is ionized , and PAH emission is seen just outside the ionized gas .
We associate the PAH emission with the photo-dissociation region of the molecular shell .